Linear motors are well known to the robotics art and are typically moved across a cooperating surface referred to as a platen. Two dimensional linear motors comprise first and second stepping motors to provide movement of the linear motor in mutually perpendicular directions, each stepping motor comprising a moving member or "forcer" which traverses a cooperating platen.
The forcer is magnetically propelled along the working surface of the platen. One typical two-dimensional forcer is the dual access X-Y motor produced by Xynetics products of Santa Clara, Calif. Magnetic propulsion is accomplished by selectively controlling the power provided to a plurality of electromagnets arranged within the forcer. The electromagnets magnetize themselves to teeth defined by a grid array machined into the working surface of the platen and comprised of a plurality of first and second groups of uniformly spaced parallel lines with the groups of lines being mutually orthogonal so as to define a regular grid matrix. The grid array grooves are preferably filled with a suitable insulating material, said grooves being formed in the surface of a ferromagnetic material or alternatively of material capable of concentrating magnetic lines of force.
In order to move two-dimensional linear motors from one position to another so that the linear motor arrives and is positioned precisely at the desired location, it is important to provide a system and/or technique in which the positioning of the linear motor is insured through a closed loop system. To date, no such closed loop system exists for accurately controlling the movement of two-dimensional linear motors.
A system presently exists which is capable of differentiating between two sets of mutually perpendicular grid lines. Each set comprises a plurality of spaced parallel lines with the two sets being of different colors. The light from a pair of sources is reflected to a pair of cooperating sensors each adapted to recognize signals of different wavelengths representing the colors of the two sets of mutually perpendicular lines. These signals are utilized to create a display upon a display means such as a CRT display of a computer monitor.
However, there are no devices capable of providing an indication that the requested movement has taken place or for providing means for accurately controlling movement through a feed back loop.